Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to an active energy hold up for power supplies and, more particularly, to an apparatus for preventing loss of power to electronic components during an interruption or drop in power.
2. Description of Related Art and Other Considerations
While the present invention was developed specifically for use in power supplies for aircraft, it is as applicable to other vehicles, such as automobiles, trucks, tanks, and the like. Therefore, while the subsequent exposition discusses aircraft, it is to be understood that the invention is likewise applicable to such other vehicles.
Power is frequently required to be supplied to electronic components, even during a momentary loss of input power or xe2x80x9cdrop outxe2x80x9d so that they will perform continuously and not be exposed to even a fleeting interruption. For example, a computer could easily shut down as a result of such an interruption and would required to be rebooted, during which time it would not be able to perform and possibly cause damage or other problems to the aircraft or its components. Similar damage or other problems result from a drop in power, for example, with a load coming onto line. This power drop would produce the same effects as an interruption in power. Therefore, an energy storage element of some form, e.g., a capacitor, is often used in concert with the power supply.
Three prior art methods are used to prevent loss of power to electronic components during an interruption or drop in power.
The most common method is to use a large capacitor bank on the input power to store energy, which is drawn upon when required.
Another method is to use a step up-step down topology (sometimes referred to as a xe2x80x9cboost-buckxe2x80x9d) with a capacitor in between the power supply and the electronics.
A third method uses one circuit to charge up a capacitor, and another to discharge the capacitor when needed. The prior art has several disadvantages.
As depicted partly in FIG. 1, power from either power source is selectively fed by a switching relay 16 to a bus line 18 to aircraft electronic components, generally designated by indicium 20. When the aircraft is on the ground and prior to engine start up, power is fed through bus 12. Start up of the engines enables electric generators connected thereto to generate power, which are then used as the power source for the electronics. During switch-over from the ground to the aircraft power source, there is a transitory interruption of power, which passengers experience as a momentary flickering of lights in the passenger compartment.
In the above first-mentioned, most common method, the energy storage capability of the large capacitor bank is poorly utilized, on the order of under 10%; therefore, the capacitor must be very large.
The above second-mentioned or xe2x80x9cboost-buckxe2x80x9d method is illustrated in FIG. 1 and depicts a system 10 for maintaining an uninterrupted supply of power to aircraft electronic components when the source of power is switched from the ground power supply to the aircraft power supply, that is, through respective buses or lines 12 and 14.
A conventional method to avoid the occurrence of an interruption and drop in power employs the use of a step up converter 22 and a step down converter 24, which are coupled to a capacitor 26. A control 28 is connected to the converters to prevent them from operating at the same time. In operation, capacitor 26 is charged while power is supplied through either of busses 12 and 14. However, if power from the busses drops or is interrupted, capacitor 26 would have sufficient storage as to continue supply to electronics 20.
In this method, the overall efficiency of the supply is lowered by at least 10% by adding a series element in the boost stage through which power must flow. This solution must be integrated into the initial design of the supply. The boost stage must handle the full supply power and, accordingly, its size is significantly impacted.
Neither of the two methods allows the selection of a capacitor voltage rating that is independent of the input voltage based, in part, upon the reason that the energy storage density of the capacitor is a strong function of its rating voltage. This results in a lack of design freedom to choose the best capacitor, and is a serious disadvantage.
The above third-mentioned method adds two new switching regulators to the circuit and, therefore, makes it significantly more complex.
The present invention overcomes these and other problems by utilizing a bi-directional converter, preferably a flyback converter, and control circuitry to regulate the converter. Once the proper voltage is reached, the circuit turns off, minimizing power consumption. When the input power drops, the bi-directional converter acts as a voltage source, keeping the supply input voltage at a minimum set point by using the energy stored in the capacitor. An anticipation circuit turns on the circuit before power is actually needed so that the response time is instantaneous.
One or more advantages may be obtained by the present invention. It allows the maximum possible utilization of the energy storage capacitor, does not effect existing supply operation, allows substantially any capacitor to be used, and is simpler than other solutions with similar performance. The relative size of the energy storage element is decreased by almost twenty-five times over that of the prior art. The circuitry minimizes the size of the energy storage capacitor, so that the charge voltage is regulated at the optimum energy storage point of the capacitor, independent of the input voltage. A high voltage capacitor can be used and, accordingly, it can store more energy per unit volume than lower voltage capacitors. This also permits about 80% of the storage energy to be extracted from the capacitor, because the bi-directional power stage delivers a regulated output voltage as the capacitor voltage is dropping.
The hold-up power converter of the present invention itself need only be designed for intermittent action; thus, it need not be large. For example, the size of a specific converter utilized in a test circuit was 2 square inches by xc2xd inch in height, corresponding to a volume of approximately one cubic inch. Its small size did not affect the advantages summarized above.
The circuit does not affect the efficiency of the main power supply inasmuch as it operates only as required to charge to energy storage capacitor. No power elements are in series with the main flow of input power. Energy shuttling and hold up is done in parallel with the main power supply function.
Close to 100% utilization of the capacitor""s energy storage potential allows any capacitor to be used. It is amenable to being added onto any existing or future supply. The invention power flows in parallel with the main power flow and, thus, only is required to handle the stored energy. This permits a freedom in design to choose the capacitor.
Other aims and advantages, as well as a more complete understanding of the present invention, will appear from the following explanation of an exemplary embodiment and the accompanying drawings thereof.